Armor plate and process of making same



i To all whom it may concern:

and HARRY L. FRE R T, citizens of the United plate to perforation and at Patented May 29, 1923.

FRANCIS BRADLEY AND HARRY L. rRRvRR'r, OF'PHILADELPHIA,

ARMoR PLATE AND PROCESS NoDrawing.

Be it known that we, FRANCIS BRADLEY States, residing at Philadelphia, Philadelphia, have invented a new and useful mentin ing Same, of which thefollowing is a full, Iclleczlir, and exact description, reference beingv a form a part of this specification.

Inan application filed by us June 27,1922, Serial No. 571,301, we set forth the discovery that if armor plate which is already treated, by known methods, to produce a plate having a hardened front with a carurized face and a .tough back, is drawn at a temperature above 500 F. and below 1100 F., so as to remove from the hard front practically all the brittleness and a large portion of thehardness, while maintaining the stiffness required to offer extraordinary resistance to displacement, it will offer greater resistance to penetration, with projectiles of the present improved type, than is offered by a plate of the ordinary type, wherein the hard front of the plate is unable to break the point of the projectile and is itself cracked and spalled off with less expenditure of power than would be required were the metal to remain in position and offer great resistance to displacement.

The object of the present invention'is to still further increase the resistance of the the same time prevent cracking under the shock of impact. I A hard faced tough backed plate of the type to which our invention is applicable may be produced, for example, by the following process, well known to those skilled in the art: An ingot of any suitable composition is cast, and after reheating is forged or rolled into a plate of a thickness about 20% in excess of the thickness desired for the finished plate. The plate, thus'formed,

county of Improveniay be reheated and annealed, or reheated to below the critical temperature and cooled either quickly or slowly. The side-of the plate intended for the face is then cleaned of all scale and a brick container built around its edges. The container is filled with a suitable carburizing compound, and a similar plate is laid face down upon it, the pair of plates being then heated to a tern Application filed June 27, 1922,

and State of Pennsylvania,

Armor Plates and Processes of Makto the accompanying drawings, which if the plate perforation or MAKINe-sAME.

Serial No. 571, 303. A

tlon of carbon into the face of the plate to the desireddepth and extent, or theplate may be carburized by a gas.

After the carburizationof the plate, by

perature andfor a time suitable for penetra-" I 1 the absorption thereby of'the desiredf'carbon, theplate is carefully cooled, and freed q of scale, the face protected by a carbonaceous covering, reheated to avery low forgingtemperature and forged to final thickness. The plate is then reheated to a temperature considerably above its criticalte'mperaturdquenched, again reheated, butitoa less degree than before and again quenched. The plate is then again reheated to a point below its critical temperature, bent and cooled slowly; below its critical temperature and quenched. The face of the plate is then heated rapidly to well above its critical temperature, while the back is kept below that temperature and the plate quenched throughout. In this heating operation, the temperature of the plate is raised to above. the criticaltempera ture to a depth substantially exceeding-the relatively thin carburized face zoneand it" is this part of the carburized face and a zone to the rear thereof, which wecall the 5 front,

In the above described, and other], well known processes of face plate, it ispresent practice to harden to a depth, in the case (say) of a 13%,- inch plate, of substantially less than five inches to not over about six inches or from thirty-five to less than forty-five per cent. of the thickness of the plate. Increase of the hardened zone, in the case of plates of the present type, would not only not give greater resistance to penetration, but would be detrimental, as 1t would provide a disproportionately thin tough back. In manufacturing our improved armor plate, however, we find that (say 13% inches in thickness) is hardened to a depth varying from substan-- tially over six inches to nearly nine inches, or' from at least forty-five per cent. to about again reheated to a point well hardening armor g sixty-five per cent. of the thickness of the plate, and is then drawn at a temperature of from 500 to 1100 degrees F. (preferably 650 degrees F.), the resistance of the plate to will be still further increased, while, by reason of the removal of the brittleness and a large portion of the hardness from the initially hardened plate, the tough or ductile zone at the back is sufficiently thick to;prevent cracking of the plate under shock of impact.

In producing initially the plate having a hard front and a'tough back, the plate may be carburized to the depth of (preferably) from seven to ten per cent. of the thickness of the plate. S uch initial face carburization is preferable in the case of most plates and where expense is not an important factor; but the benefits and advantages of our invention, to a substantial degree, are secured without initial face carburization.

Our plates may therefore have a substantially uniform carbon content.

It is not intended to limit the present invention to face carburization, but to claim the invention broadly whether or not'the plate is face carburized and also to claim the more specific invention wherein the plate is of substantially uniform carbon content. In an application filed of even date herewith, Serial No. 571,302, we have described and claimed an invention having the same essential features as those herein set forth but restricted to face carburization of the plate, such invention being both a specific modification of the present invention and an embodiment of and improvement upon the application filed by us of even date herewith, Serial No. 571,301. 7 V

This application is a continuation in part of application Serial No. 505,889, filed October 6, 1921.

Having now fully described our invention, what we claim and desire to protect by Letters Patent is- 1. The process of so treating armor plate as to render it resistant to perforation, which comprises treating the plate to produce a tough back and a front hardened to a depth of from forty-five to sixty-five per cent. of the thickness of the plate, and then drawing the plate at a temperature not below 500 degrees F. nor above 1100 degrees F.

2. The process of producing armor plate so as to render it resistant to perforation, which comprises treating a plate of substantially uniform carbon content to produce 'a tough back and a front hardened to a depth of from forty-five tOSlXbY-fiVG per cent. of the thickness of the plate while maintaining the uniform carbon content of the plate, and then drawing the plate at a temperature not below 500 degrees F. nor above 1100 degrees F. 1

3. As a new article of manufacture, an armor plate provided with a tough back and a stiff hardened front from which the normal brittleness has been substantially removed and whose normal hardness has been substantially diminished, the depth of the de-brittled, stifl zone of reduced hardness being from forty-five to sixty-five per cent. of the thickness of the plate.

a. As a new article of manufacture, an armor plate of substantiallv uniform carbon content provided with a tough back and a stifl' hardened front from which the normal brittleness has been substantially and whose normal hardness has been substantially diminished, the depth of the debrittled, stiff Zone of reduced hardness being from forty-five per cent. to sixty-five per cent. of the thickness of the plate.

In testimony of which invention, we have hereunto set our hands, at Philada, Penna, on this 21st day of June, 1922.

FRANCIS BRADLEY. HARRY L. FREVERT.

removed 

